Polypropylene is in use in many fields because of its superior mechanical properties, clarity, chemical resistance and processability. However, polypropylene has a disadvantage of being poor in impact resistance at low temperatures. Several methods have been proposed in order to overcome this disadvantage, such as incorporating polypropylene with polyethylene (Japanese Patent Publication No. 6975/1962), incorporating polypropylene with a solid propylene-ethylene copolymer containing 30 to 70 wt% of ethylene (Japanese Patent Publication No. 7088/1960), incorporating polypropylene with polybutene (Japanese Patent Publication No. 2245/1959), and incorporating polypropylene with polyisobutene (Japanese Patent Publication No. 10640/1960).
The above-mentioned methods are effective at improving the low-temperature impact resistance of polypropylene, but only at the sacrifice of polypropylene's inherent clarity. Therefore, the polymer products cannot be applied to the production of film or sheet or blowmoldings for food-packaging that requires clarity.
On the other hand, there is disclosed in Japanese Patent Publication No. 25693/1983 a composition composed of polypropylene, low-density polyethylene, and an amorphous ethylene-1-butene polymer or amorphous ethylene-propylene copolymer resulting from polymerization by a catalyst system consisting of a soluble vanadium compound and an organoaluminum compound. This composition is good in clarity but is decreased in stiffness and is not necessarily satisfactory in impact resistance.